1. Field of the Invention
The present invention relates to a semiconductor laser apparatus for an optical head for performing beam radiation and incident beam detection.
2. Description of the Prior Art
An optical head used in an optical recording/reproducing system or the like irradiates an optical recording medium with a beam, and detects a modulated beam from the optical recording medium to perform information recording/reproducing.
The optical head normally uses a semiconductor laser apparatus. FIG. 1 shows an optical head using a typical conventional semiconductor laser apparatus.
In an optical head 1, a beam 4 radiated from a semiconductor laser 2 and reflected by a beam splitter 3 is incident on an optical recording medium 6 through an objective lens 5. The beam 4, reflected by the optical recording medium 6 and passing through the objective lens 5 and the beam splitter 3, is incident on a photodetector 7.
In the optical head 1, the semiconductor laser 2, the beam splitter 3 and the photodetector 7 constitute a semiconductor laser apparatus 8.
In the conventional semiconductor laser apparatus 8, positional adjustment of the three separate optical components results in a high cost for the optical head 1.
In addition, the optical head scans the optical recording medium without contact, so focus servo control is required. An astigmatism method is largely used as a method of detecting a focus error. In this case, since a cylindrical lens 9 is normally arranged between the beam splitter 3 and the photodetector 7, the above problem becomes even more severe.